Heretofore, an expansive admixture, a drying shrinkage reducing agent and a limestone aggregate or the like have been used to suppress cracking caused by shrinkage of mortar and/or concrete, in which case, however, an increase in the cost is caused.
Examples of a commercially-available shrinkage reducing agent for concrete include a concrete admixture for ready-mixed concrete (by Taiheiyo Materials Corporation, under the trade name “Taiheiyo Tetra-guard AS21”, for instance), which mainly contains a lower alcohol-alkylene oxide adduct.
Meanwhile, examples of a commercially-available shrinkage reducing agent applied to the surface of hardened concrete and/or mortar in order to reduce drying shrinkage of such concrete and/or mortar include a coating-type shrinkage reducing agent (by Flowric Co., Ltd, under the trade name “Nutte-guard” (a registered trademark), for instance), which mainly contains such components as a glycol ether-based derivative which is a type of nonionic surfactant.
A patent document 1 as one of the prior art documents, for instance, discloses a method of preventing the occurrence of cracking by impregnating the inner surface of a rectangular precast product with an organic drying shrinkage reducing agent such as a nonionic surfactant.
Other patent documents 2 to 5 disclose the arts relating to coating and/or impregnation treatments with a surface modifying agent for improvement in quality of concrete.
Besides, a non-patent document 1 states that urea is effective as a concrete admixture to reduce thermal cracking and/or drying shrinkage cracking of concrete after hardened, and also states various properties of concrete using urea on the basis of some experimental results.